Gadenin日本語Get the appWater depth is the main control you have
For a crop with a reputation for being complicated, rice asks for very little in a tub. There is nothing to stake, nothing to prune, nothing to train and no pollinating to do by hand. What there is, almost entirely, is water depth, and the depth is not one number. It changes with the stage of the plant, and getting it roughly right at each stage is most of the difference between a tub that fills with heads and a tub that stays leafy and disappointing.
Check the tub daily in hot weather. A wide, shallow container in full sun in high summer can lose an inch (2.5 cm) a day to evaporation and transpiration together, and rice is thirstier than it looks because a full tub is a solid block of leaf. Top up with a gentle stream aimed at the side of the container rather than at the mud, so you do not scour a hole and expose roots.
| Stage | Water depth | Why |
|---|---|---|
| First week after transplanting | 1 inch (2.5 cm) | Deep water floats new clumps out before they anchor. |
| Establishment to active tillering | 2 to 4 inches (5 to 10 cm) | Suppresses weeds and buffers night temperature while the fan of stems builds. |
| Midsummer, tillering finished | Drained, mud damp | The deliberate dry-down. Stops useless late stems and firms the root plate. |
| Heading and flowering | 3 to 4 inches (8 to 10 cm) | The thirstiest weeks. Drying out now costs you filled grain directly. |
| Grain filling to ripening | 1 to 2 inches (2.5 to 5 cm) | Enough to keep filling going, shallow enough to start hardening the crop. |
| Final two to three weeks | Drained | Dry mud ripens the grain evenly and makes the harvest dig far easier. |
Tillering, and the midsummer drain
A few weeks after transplanting each seedling starts throwing new shoots from its base. This is tillering, and it is where the crop comes from: a clump of three seedlings can become a fan of twenty or thirty stems, and each stem that matures in time carries one head. Watch the fan widen through early summer. That widening is the single best sign that the tub is happy.
It does not stop on its own at a useful point. Left flooded, the plant keeps producing late tillers that will never have time to make a head, and they take light and nutrition from the ones that will. So once the clumps look full, roughly when you count twenty or so stems in a clump and the surface of the tub has closed over, deliberately let the water go. Stop topping up and let the surface drain or evaporate until the mud is damp and just starting to firm underfoot, and hold it there for about a week. Hairline cracks in the surface are the signal you have gone far enough.
This dry-down looks like neglect and feels wrong the first time. It does three things: it stops the wasteful late tillers, it forces oxygen into mud that has gone stale and sour after weeks underwater, and it makes the plants anchor harder, which is your main defense against the whole tub flattening in a late-summer storm. Then reflood and carry on.
If the leaves roll into tight tubes lengthwise during the dry-down, you have gone too far. Reflood the same day. A little leaf rolling in the hottest hour of the afternoon is normal and recovers by evening.
Feeding: a little, and at the right moment
Rice in a tub is not a hungry crop, and overfeeding it is the classic home-grower mistake. Too much nitrogen early gives you a magnificent stand of dark green leaf, weak stems, and a plant that falls flat under its own weight the moment the wind gets up. It also makes the crop far more attractive to sap-feeding insects.
- Start lean at transplanting A modest amount of balanced fertilizer worked into the mud is enough for the first six weeks. Rice draws nutrients out of flooded soil more efficiently than most plants do out of dry soil.
- Feed once when the fan of stems is full A light dose of balanced feed at the end of tillering, just before or just after the dry-down, supports the stems that are going to carry heads. Sprinkle it on the mud rather than dissolving it in the standing water.
- Feed once more as heads emerge A second light dose when the first heads push out of the stems goes directly into filling grain. This is the feed that most changes what you actually harvest.
- Stop entirely once grain starts to harden Late nitrogen delays ripening, softens the straw and invites disease. From the moment the heads start to tip over, feed nothing.
Reading the plant, and what to record
Yellowing on the oldest, lowest leaves through the season is normal and expected; the plant is moving nitrogen up to where it is needed. Yellowing that starts on the newest leaves at the top is not normal and usually means the mud has gone anaerobic and sour, which you can smell as a rotten-egg note when you stir it. Drain, let it air for a couple of days, stir the surface, and reflood.
Algae is the other constant. A green film on the water is harmless and even useful shade early on, but a thick blanket that lifts and traps seedlings needs skimming off with your hand. It builds fastest where the water is warm, shallow and over-fertilized, which is another argument for feeding the mud rather than the water.
Keep a short running note of the date tillering visibly started, the date you drained for the dry-down, the date the first head emerged, and the number of stems in one marked clump. Those four entries turn a vague memory of a good or bad year into something you can act on. If heading came late and the grain never hardened before the cold, next year you start the seed tray earlier. If the tub lodged, you fed too early or planted too close, and the stem count in your marked clump will tell you which.